The Coastal Range in the Mediterranean segment of the Chilean active margin is a soil mantled landscape able to store fresh water and potentially support a biodiverse native forest. In this landscape, human intervention has been increasing soil erosion for ∼200 yr, with the last ∼45 yr experiencing intensive management of exotic tree plantations. Such intense forest management practices come along with rotational cycles as short as 9-25 yrs, the construction of dense forest road networks, and the fostering of wildfire susceptibility due to the high amounts of fuel provided by dense plantation stands. Here we first compare decadal-scale catchment erosion rates from suspended sediment loads with a 10^4-years-scale catchment erosion rate estimated from detrital 10 Be. We then explore these erosion rates against the effects of discrete disturbances and hydroclimatic trends. Erosion rates are similar on both time scales, i.e. 0.018 ±0.005 mm/yr and 0.024 ±0.004 mm/yr, respectively. Recent human-made disturbances include logging operations during each season and a dense network of forestry roads, which increase structural sediment connectivity. Other disturbances include the 2010 M w 8.8 Maule earthquake, and two widespread wildfires in 2015 and 2017. A decrease in suspended sediment load is observed during the wet seasons for the period 1986-2018 coinciding with a decline in several hydroclimatic parameters. The low 10^4-years erosion rate agrees with a landscape dominated by slow soil creep. The low 10-years-scale erosion rate and the decrease in suspended sediments, however, conflicts with both the observed disturbances and increased structural (sediment) connectivity. These observations suggest that, either suspended sediment loads and, thus, catchment erosion, are underestimated, and/or that decennial sediment detachment and transport were smeared by decreasing rainfall and streamflow. Our findings indicate that human-made disturbances and hydrometeorologic trends may result in opposite, partially offsetting effects on recent sediment transport.

A geomorphological key paradigm predicts that intact forests are erosional idle, however comprise an efficient weathering machine sustaining high soil production rates. Only during times of disturbance, e.g., by earthquakes, those forests are observed to jump up to high-erosion-state, then being capable of releasing some of Earth’s highest sediment yields involving massive pulses of organic carbon. Coastal temperate rainforests, in particular, do not only store unparalleled carbon stocks building up a globally important carbon sink, but are also home to high (endemic) biodiversity. Here we document extraordinarily high catchment-averaged denudation rates, across multiple disturbance cycles, under the dense vegetation of the Patagonian rainforests. There, 10 Be-derived denudation rates of >0.8 m kyr^-1 exceed any known value from the entire Chilean Andes orogen, a highly variable >3.000 km long natural laboratory involving steep climatic and topographic gradients. We argue that such high denudation rates are consistent with a first-order control of the rainforest itself. High biomass loads exert a soil surcharge that promotes landsliding already along a relatively low critical slope angle. In contrast, denudation rates from more arid, and less forested sectors of the Chilean Andes though going along with steeper critical slope angles remain below half of our new rates derived from the Patagonian rainforests. Taken together, our study provides indication that denudation, to a higher degree than hitherto agreed on, operates as a continuous process involving soil production, vegetation, physical erosion and ecohydrological processes. Such a holistic denudational continuum, finally, is different from prevailing views that vegetation generally stabilizes hillslopes, thus promoting steep slope gradients, however, limiting landsliding activity.